content: /**
   * Copyright (c) 2016-present, RxJava Contributors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
   * compliance with the License. You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software distributed under the License is
   * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
   * the License for the specific language governing permissions and limitations under the License.
   */
  
  package io.reactivex.observable.extensions;
  
  import io.reactivex.common.annotations.*;
  
  /**
   * A minimalist queue interface without the method bloat of java.util.Collection and java.util.Queue.
   *
   * @param <T> the value type to offer and poll, not null
   */
  public interface SimpleQueue<T> {
  
      /**
       * Atomically enqueue a single.
       * @param value the value to enqueue, not null
       * @return true if successful, false if the value was not enqueued
       * likely due to reaching the queue capacity)
       */
      boolean offer(@NonNull T value);
  
      /**
       * Atomically enqueue two values.
       * @param v1 the first value to enqueue, not null
       * @param v2 the second value to enqueue, not null
       * @return true if successful, false if the value was not enqueued
       * likely due to reaching the queue capacity)
       */
      boolean offer(@NonNull T v1, @NonNull T v2);
  
      /**
       * Tries to dequeue a value (non-null) or returns null if
       * the queue is empty.
       * <p>
       * If the producer uses {@link #offer(Object, Object)} and
       * when polling in pairs, if the first poll() returns a non-null
       * item, the second poll() is guaranteed to return a non-null item
       * as well.
       * @return the item or null to indicate an empty queue
       * @throws Exception if some pre-processing of the dequeued
       * item (usually through fused functions) throws.
       */
      @Nullable
      T poll() throws Exception;
  
      /**
       * Returns true if the queue is empty.
       * <p>
       * Note however that due to potential fused functions in {@link #poll()}
       * it is possible this method returns false but then poll() returns null
       * because the fused function swallowed the available item(s).
       * @return true if the queue is empty
       */
      boolean isEmpty();
  
      /**
       * Removes all enqueued items from this queue.
       */
      void clear();
  }
  